Mechanically-stoked furnace



AfHOFMANN. MECHANICALLY STOKED FURNACE. APPLICATION FILED OCT. 31. 1918.1,388,714. I Patented Aug. 23, 1921.

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MECHANICALLY STOKED FURNACE. APPLICATION FILED OCT. a1, 1918.

1,388,714. Patented'Aug- 23, 1921.

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ALFRED HOFMANN, OF ZURICH, SWITZERLAND.

MECHANICALLY-STOKED FURNACE.

Application filed October 31, 1918.

T 0 all whom it may concern Be it known that I, ALFRED HOFMANN, acitizen of the Republic of Switzerland re siding at 7 Asylstrasse,Zurich, in the anton of Zurich, Republic of Switzerland, have=inventedcertain new and useful Improvements in Mechanically-stoked Furnaces; andI do hereby declare the following to be a full, clear, and exactdescription of tl'ie invention, such as will enable others skilled inthe art to which it appertains to make and use thesame, reference beinghad to the accompanying drawings, and to letters of reference markedthereon, which form a art of this specification.

his invention has for its 0b3ect to provide an improvedmechanically-stoked furnace.

According to this invention the improved furnace includes two or moretravellng grates arranged one above the other in such a manner that eachlower traveling g'ate receives the fuel dropping from an upper travelinggrate and is adapted to convey away the slag and ashes.

F igure 1 is a side view of a furnace provided with my improvements. Inthis view certain parts are shown in section, certain parts areshowndiagrammatically and other parts are shown partly broken away forthe sake of clearness.

In the accompanying drawings Fig. 2 is an end view of the furnace.

Fig. 3 is a front elevation with parts in section taken on thelinel-II-III-IV- V-VI of Fig.1.

Fig. 4: is a diagrammatic detail sectional view of oneof the travelinggrates.

Fig. 5 is a transverse vertical sectional detail view of the mechanismshown in Fig. and illustrating means for air cooling one of the plateswhich is arranged on the side of the fire-box to prevent the slag fromadhering to the sides of the brickwork casing of the furnace.

Fig. 5 is a view similar to Fig. 5 but showing a modification in whichthe plate is' water-cooled.

Figs. 6 and 7 show a side view and sectional View respectively of thepawl and ratchet mechanism used in driving one of the grates.

Fig. 8 is a side view of the pawl and ratchet mechanism used in drivingthe other grate.

Specification of Letters Patent.

Patented Aug. 23, 1921.

Serial No. 260,560.

Fig. 8 is a detail end View of the pawl mechanism for driving the lastmentioned grate.

Fig. 9 is a diagrammatic sectional view of a modified form of theinvention.

Fig. 10 is a top planview of a couple of the flap plates used forpreventing the entrance of an excessive amount of air at the exit end ofone of the grates.

Referring first to Figs. 1 to 8 and 10, the fuel is charged into ahopper 1 from which it is delivered by a power-driven feeder 2 of knowntype and an inclined plate 3 on to the upper traveling grate 5. In orderto prevent pieces of coal from rolling down and the advancing coal frombecoming too highly heated a damper 4 is pro vided which is adapted tobe operated from the outside and serves also to prevent entrance of thehot gasesinto the fuel-feed passage. This damper is raised when fuel isbeing fed on to the grate 5. The fuel is carried along by the grate 5and then drops on to the lower t aveling grate 6. During this advancethe fuel is pre-heated, gasified and ignited by the forwardly deflectedfire gases (indicated by the arrow I), the resulting smoldering orpartial combustion causing at first an increase in its volume andafterward a decrease in its volume when the fuel has become completely,degasified.

In passing from the upper grate on to the lower grate the layer of cakedfuel is broken up and turned by the outwardly opening grate bars insomewhat the same manner as is done in hand-etching with a poker for thepurpose of loosening the layer of fuel.

The removal of the slag takes place at the exit end of the lower gratewhere the slag is removed continuously as the grate travels. The largerpieces of coal pass on to the lower grateG while still only in the firststage of combustion, whereas the smaller pieces, the dust and the smallcoal have had suflicient time to be completely burned. The result ofthis is a diminution in the volume of the burning fuel so that, as isgenerally the case with traveling grates, vacant spaces or holes occurin the layer of burning fuel tl'irough which an injurious excess of airpasses up through the fuel. For the purpose of diminishing these holesand the losses occasioned thereby, and so as to keep the lower gratealways completely covered,

the speed of the lower grate is reduced as hereinafter describedrelatively to the speed of the upper grate in proportion to thediminution in volume of the fuel layer in such a manner that the largepieces shall also be completely burned, and that only slag, that is onlyincombustible matter, shall drop off at the rear.

In order to prevent the entry of an injurious excess of air at the pointwhere the slag is removed, freely movable depending flaps 7 are providedat the exit of the lower grate. These fiaps are caused by their ownweight to bear against the grate bars and thus act as a closure againstthe entry of air in all positions of the grate. When a third grate 6' isemployed, as shown in ,Fig. 9, for carrying away the slag and travelstherefore only at a very low speed, the flaps 7 are provided at thethird grate and the layer of slag is kept sufficiently high to preventany entry of air between the two grates.

ries a fixed constant-throworank 11.

In order to prevent the slag from adhering to the sides of the brickworkcasing of the furnace, both the longitudinal sides of the grate areprovided with metal plates 8 or 9 which are prevented from burning bybeing cooled by means of air as at 8, or water as at 9. The residues,such as slag and ashes, are removed from underneath the grate by aconveyer 6 and raised to a point whence they can be taken away by hand.

The furnace mechanisms are driven from a pulley 10 fixed on a shaft 10.This shaft carries a fixed gear 1O that drives a gear 10 fixed on ashaft 10, which also car- This crank imparts a constant throw through aconnecting rod 12 and a lever 13 to a pawl 14. The lever 13 is looselymounted on a shaft 15. Since the amount of coal to be burned must bevaried to suit the steam consumption, it is necessary to varyaccordingly the speed of the ratchet wheel 16, which is fixed on theshaft 15 and controls all the mechanisms. This variation is effected byarranging the pawl 14 to slip idly over more or less of the periphery ofa shield 17 when a reduced steam production is desired. By this meansthe speed of the shaft 15 may be varied at will from nil to the maximum,and the feed and removal of the fuel may be regulated according torequirements. The alteration in the position of the shield 17 iseffected by means of a piston 19 working in a cylinder 19' and beingunder the influence of boiler pressure through the medium of the pipe19". This piston moves up when the boiler pressure rises and descendswhen the boiler pressure falls. The movement of the piston istransmitted, by rods 21 connectedto the piston rod 20, to a lever 23fulcrumed on the shaft 22. One end of the lever is connected by a rod120 to the shield 17 and the other shifting of the lower shield 17 isefiected from the upper shield 17 through the medium of the connectingrod 28 which may be lengthened or shortened by means of a threadedsleeve 28*, whereby the shield 17" can be given more or less lead overthe upper shield 17, and thus the speed of the grate 6 can be reduced asdesired relatively to the speed of the upper grate 5.

The grates are driven by means of worm gears 29 mounted on the shafts 15and 15.

hese gears engage worm gears 29 fixed to the drive shafts of the grates.

The shaft 15 also supplies the motion for driving the mechanismactuating the fuel feeding apparatus 2 and the slag-removing conveyerunderneath the grates 5 and 6. By thi means all the drives for adaptingthe combustion to the steam consumption are derived from a single shaft15. As above stated the rates are constructed as traveling grates or thepurpose of preventing the losses that occur with ordinary rates due tosmall coal dropping through. he transversely arranged grate bars 30 areheld at both ends in chains 31 by means of noses 32, 33 projecting fromthe inner fishplates of the chains, and are kept from falling out wheninverted by means of pins 34.

As the grate bars pass over the chain wheels the bars 0 en outwardly andthus form wide spaces etween the bars whereby the layer of caked fuel isbroken up.

The improved furnace may be a plied to various types of boilers but inthe drawings I have shown it applied to a flue boiler.

In the modification illustrated in Fig. 9, the fuel drops from thesecond slightly upwardly inclined traveling grate 6 on to a likewiseinclined third traveling ate 6 whose speed is somewhat less than t espeed of the grate 6.

What I claim is 1. In a furnace, an inclined upper traveling grate, alower traveling grate extending partially beneath the u per grate and receiving the fuel direct y dropping from the upper grate and conveyingaway the slag, means for driving the travelin rates at adjustabledifferent s ds, and ioiler steam controlled means or regulating the airsupply and the conveying away of the slag to suit the steam consumption.

2. In a furnace, an inclined upper traveling grate, a lower travelinggrate extending partially beneath the upper grate and receiving the fueldirectly dropping from the upper grate and conveying away the slag,

a rotatable shaft, a crank actuated by said shaft, a main shaft fordriving the upper traveling grate, a ratchet mechanism placed on themain shaft and actuated by the crank to impart to the shaft a step bystep movement, a shield loosely mounted on the mainshaft, automaticmeans actuating said shield to vary the extent of said step by stepmovement for causing the main shaft to be driven automatically atdifferent speeds, a third shaft for driving the lower traveling grate, aratchet mechanism placed on the said shaft and actuated by the saidcrank to impart to this shaft a step by step movement, a shield looselymounted on the third shaft and connected to the first mentioned shieldfor automatically varying the extent of the last mentioned step by stepmovement for causing the third shaft to be driven automatically atdifferent speeds.

In testimony whereof, I have signed my name to this specification.

ALFRED HOFMANN.

